Wireless telecommunication networks are well known and widely deployed. The 3rd Generation Partnership Project (3GPP), a collaboration of telecommunications standard development organizations, publishes and maintains the technical standards defining the structure and operation of modern wireless telecommunication networks. Long Term Evolution (LTE) is a 3GPP standard for a 4th generation (4G) wireless communication network based on GSM/EDGE and UMTS/HSPA network technologies. LTE is specified in 3GPP Releases 8-10, and has been deployed since 2010. LTE support high data rates and low latency, and features all-IP network architecture, with only eNode B (base station) fixed nodes in the RAN, providing wireless communication service to a plurality of user equipment (UE), such as cellular telephones, smartphones, mobile/tablet computers, and the like. LTE supports numerous options to increase flexibility of deployment, including time (TDD) or frequency (FDD) division duplex operation; spectrum flexibility with support for 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz bandwidth carriers; the coexistence of macro, femto, and pico cells covering varying geographic areas; and support for advanced operating technologies such as high speed shared packet channels, MIMO operation, and carrier aggregation.
FIG. 1 depicts a high-level, functional block diagram of an LTE wireless communication network 10. A Radio Access Network (RAN) 12, e.g., E-UTRAN, comprises one or more base stations 14, known in LTE as eNodeBs. Each eNodeB 14 provides wireless communication service to a plurality of User Equipment (UE) 16 within a geographical area, or cell 18. A core network 20 comprises a plurality of communicatively-linked nodes, such as a Mobility Management Entity (MME) and Serving Gateway (S-GW) 22. The MME/S-GW 22 connects to numerous nodes (not all of which are depicted for simplicity), including a Packet Data Network Gateway (PDN-GW) 24. The PDN-GW 24 provides connectivity to packet data networks such as the Internet 26, and through an IP Multimedia Subsystem (IMS) 28 to the Public Switched Telephone Network (PSTN) 30.
LTE uses Orthogonal Frequency Division Multiplex (OFDM) modulation in the downlink, and DFT-spread OFDM in the uplink. The basic LTE downlink physical resource can thus be seen as a time-frequency grid as illustrated in FIG. 2. Each resource element corresponds to one OFDM subcarrier (15 KHz) during one OFDM symbol interval.
In the time domain, LTE downlink transmissions are organized into radio frames of 10 ms, each radio frame consisting of ten equally-sized subframes of length Tsubframe=1 MS, as illustrated in FIG. 3.
Resource allocation in LTE is described in terms of resource blocks (RB), where a resource block corresponds to one slot (0.5 ms) in the time domain and 12 contiguous subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth.
Carrier aggregation (CA) is a way to dynamically increase the bandwidth available to a UE. In carrier aggregation, up to five spread-spectrum carriers, referred to as component carriers (CC), may be assigned to a UE. For example, FIG. 4 depicts five 20 MHz carriers aggregated to achieve 100 MHz of bandwidth. In general, the component carriers may be of different bandwidths, and may be contiguous or non-contiguous in frequency. Carriers may be aggregated in the uplink (UL) as well as downlink (DL), although the number of UL carriers must be equal to or less than the number of DL carriers. Component carriers are also referred to as cells (not to be confused with the use of that term to describe the geographic extent of a base station's coverage). Each UE in CA has one primary serving cell (PCell), and may be assigned as many secondary serving cells (SCell) as the UE is able to support.
To perform link adaptation, in which the modulation, coding, and other signal and protocol parameters are selected to match the current radio link conditions, a serving base station must obtain information about the downlink channel quality. It obtains this information through Channel State Information (CSI) reports from UE, which assesses the DL channel by processing reference symbols (also known in the art as pilot symbols) transmitted in the DL, of which the data pattern are known a priori. LTE defines both periodic and aperiodic CSI reporting. Aperiodic reports are more desirable for DL adaption due to the flexibility on demands of scheduling time and a larger report size, which may carry more information. An aperiodic CSI report is sent over Physical Uplink Shared Channel (PUSCH) and is scheduled by eNodeB when deemed necessary. The aperiodic CSI report for a UE can be sent without uplink data, which is referred to as a stand-alone aperiodic CSI report. A stand-alone CSI report is scheduled either because the uplink channel condition is not good enough for data and control information multiplexing, or because the UE has no UL data to send when the eNodeB requires updated DL channel conditions for DL data transmission.
LTE specifies that when a UE is in carrier aggregation, and aperiodic CSI reports for multiple serving cells are scheduled in the same subframe, the UE shall concatenated all the cell CSI reports into one single aggregated CSI report. 3GPP Release 10 specifies a CSI request field by which an eNodeB requests CSI from a UE in carrier aggregation, by requesting CSI for its own DL link, or for one of two sets of serving cells; the sets are configured by higher layers, such as Radio Resource Control (RRC) signaling.
For stand-alone aperiodic CSI report, LTE allows up to 4 RBs for single serving cell CSI report and up to 20 RBs for multiple serving cell CSI reports, with no further specification or restriction. An LTE network could achieve more robust and bandwidth-efficient scheduling with a systematic approach, at the eNodeB, for the scheduling, bandwidth allocation and link adaptation of stand-alone aperiodic CSI reports by UE in CA.
The Background section of this document is provided to place embodiments of the present invention in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.